The benign monsters in these 25 poems are guaranteed to be cheerfully scary. Included in the motley group is the ugstabuggle, ``a monster nearly nine feet tall / With hairy, grasping hands'' who conveniently disappears when you stop thinking of him. The Marog from Mars has ``a body of brass / And seventeen fingers and toes'' and would make an entire classroom shriek, if anyone could see him. And the ``great huge horrible horrible / creeping up the stars'' is, well, HORRIBLE. Rees's watercolors of wide-eyed children and twitchy goblins are just frightening enough to provide thrills without causing nightmares. A mixture of such British and American poets as e. e. cummings, Lilian Moore, Ted Hughes and Shel Silverstein provides verses bound to provoke shivers and giggles. From the hilariously hungry Alphabet Monster who might eat Y-O-U to the lovable snaggle-toothed bat, Rees's creatures are wickedly entertaining. Ages 4-8. (Oct.)